There are quite a few things I could tell you about Dr. Charles Miller, a retired physician in Wilmington, Delaware, who has made dozens of trips abroad to care for the world’s impoverished peoples. But what I want to concentrate on today is Dr. Miller’s ability to adapt easily to changes in plans. This is a skill I’d like to hone, especially during busy times. The holidays, for example.

I met Dr. Miller when my father suggested I speak with him about his experiences in international health care. In 1999, after 30 years as a pediatrician, Dr. Miller settled into what he hoped would be a happy retirement with his beloved wife. He was 70. A year later his wife suffered an internal hemorrhage that left her with a brain injury. Two years later she died.

I don’t want to give the impression that Dr. Miller adapted to this initial change of plans with ease. Quite the opposite. For nine months he lived in what he describes as the deepest sorrow imaginable.

One day he received a magazine in the mail that advertised a “Weekend for Renewal” at the Cove, the retreat center in Asheville, North Carolina, run by Billy Graham. He signed up for it without reading any details.

At the Cove, he was surprised to learn that the weekend program focused on World Medical Missions, the Graham organization that provides short-term medical care to struggling people in poor countries. On a hike through one of the retreat center’s deep forests, Dr. Miller says God spoke to him. “He told me, you asked me to open a door. This is it.”

He signed up for a trip with the organization, and then another. When we spoke in 2012, he had served as a staff physician on 38 trips, “and counting.” At age 83 he was then beginning to scale back. His schedule for the year included “only” trips to Zambia, Cameroon, and South Sudan.

“The fact was that I was depressed,” he said, and working with World Medical Missions “lifted me. I’ve kept floating for twelve years.”

Dr. Miller with a child in Haiti after the 2010 earthquake.

Dr. Miller and I spoke in his apartment, which was filled with artwork from the countries he’s visited. Thoughtful and fit, with wire-rim glasses and a polo shirt, he seemed to relish talking about his experiences.

Our discussion was wide-ranging. He listed the world’s two biggest health problems as “number one, clean water; and number two, sanitation. If you could take care of those, the rest would fall into place.” Simple steps like providing kids with folic acid would also make a huge difference, he added. “And nutrition. They eat mostly corn meal, which is packed with calories but no food value.”

Although he found the work uplifting, especially when he was able to cure children, it was not easy. On his first trip, to Zambia, “I had six or seven children die. In all my professional practice (in the U.S.) I can’t remember having that many children die.” It was a challenge to keep his emotions in check so he could turn his full attention to the next patient. “It still hurts when a child dies. I don’t ever want to get to the point where I don’t feel. And the problem is that you get them well and send them right back into the same miserable situation.”

Despite the challenges, he loved the work. Bit by bit it changed his entire approach to life. Before, he would habitually worry about the details: what was going to happen next, what he would eat, who he would encounter, how much time it would take. Now, though, “I move through the world without worry, and the Lord takes care of me.” Things simply unfold.

“If my plane’s late and I miss a connecting flight, it’s okay. I get there a little later. I stay overnight in a place different from where I’d planned.”

“Sometimes,” I said, “those kinds of delays allow you to meet someone you wouldn’t have met otherwise. They open up opportunities for really interesting encounters.”

“I’ve had that happen,” he agreed.

I have too, many times. Just last week a series of events left me in the company of a homeless man who, I learned, had lost his 26-year-old son in a car accident. We talked for a long time, and hugged when we said goodbye.

Relaxing into life, learning to live in the moment, is said to be one of the best things we can do for our mental and spiritual health. This teaching is deeply rooted in Eastern practices, including Buddhism. It’s intriguing to me that Dr. Miller, an evangelical Christian, counts slowing down and abandoning worry as one of the great benefits of serving others. Until our conversation, he said he hadn’t thought of it as “living in the moment—but yes, that’s what it amounts to.”

Dr. Miller kept working with World Medical Missions through 2014. But a case of deep vein thrombosis prevented him from making a trip to China last April, and he decided to retire from the work. His leg immediately healed. “You know what I’m going to say about that,” he laughed. “The Lord told me it was time to quit, and when I did He took away the thrombosis.”

I don’t have the skills for the type of missionary work Dr. Miller so generously offered to the impoverished people of the world. I believe I have a capacity for empathy and kindness, which by themselves can be great gifts. In this busiest of seasons, may I remember to relax, breathe, and strive to live second by second—with the hope of encountering someone intriguing, or possibly in need, whom I otherwise might simply breeze by.